1. Field of the Invention
The present invention relates to an adaptive antenna apparatus for mobile communication mainly for use in a communication equipment such as a mobile telephone or a radio communication apparatus. In particular, the present invention relates to an adaptive antenna apparatus including an adaptive controller for adaptively controlling at least two antenna elements.
2. Description of the Related Art
In recent years, mobile radio communication apparatuses such as mobile telephones have been rapidly downsized and thinned. Further, the mobile radio communication apparatuses are not only used as conventional telephones, but have also been transformed into data terminal devices for transmitting and receiving electronic mail and browsing websites on the WWW (World Wide Web). A volume of information handled by the mobile radio communication apparatus, which conventionally used to include audio and characters, now contains photographs and moving images therein resulting in a large capacity. Thus, a further improved quality is demanded in the communications. Under the circumstances, it has been proposed to adopt an adaptive antenna apparatus in a mobile terminal, whose main purpose is conventionally to increase a performance of an antenna in a base station (for example, See Japanese Patent Laid-Open Publication No. 11-284424, which is hereinafter referred to as a Patent Document 1).
FIG. 17 is a block diagram showing a configuration of an antenna apparatus for use in a mobile terminal according to a first prior art, which is disclosed in the Patent Document 1. The first prior art is directed to resolve problems such as electric power being converted into heat and being transmitted onto a head part of a human body, which fails to contribute to the communication to be unnecessary, and a reception characteristic deteriorates since delay waves interfere with each other. To this end, the first prior art is provided with an electrically conductive housing 71, a plurality of antenna elements 72, a transmission and reception circuit 73, and an amplitude and phase adjusting circuit 74 for decreasing the electric power radiated onto the head of the human body by adjusting the amplitudes and the phases of the antenna elements 72. According to the configuration, the electric power radiated onto the head part of the human body is reduced at the time of the transmission, and signals transmitted to the antenna elements 72 can be efficiently radiated into a space. On the other hand, the efficiency can be effectively improved since an antenna directivity in any direction other than that toward the human body can be increased in the absence of the directivity toward the human body with respect to the mobile terminal at the time of the reception.
There is another proposed configuration where nulls of the directivity are directed in directions of the delay waves of interference waves, in order to eliminate the interfering delay waves (for example, See Japanese Patent Laid-Open Publication No. 10-242739, which is hereinafter referred to as a Patent Document 2). FIG. 18 is a block diagram showing a configuration of a base station antenna apparatus for a mobile communication according to a second prior art disclosed in the Patent Document 2. In the second prior art, the base station antenna apparatus for the mobile communication is constituted as follows in order to prevent the interference of the delay waves and reduce the number of the antenna elements in the case of employing an array configuration to realize a pencil-shaped beam. The second prior art relates to the base station antenna apparatus for use in the mobile communication which radiates a strip-shaped region, where a plurality of antenna elements 81 are linearly arranged to be perpendicular to the longitudinal direction of the strip-shaped region, and the parameters of the antenna elements 81 are set as follows. The antenna elements 81 has a number of elements, which is equal to or larger than two elements, and is equal to or smaller than five elements, and an interval S between the antenna elements 81 is set to equal to or larger than one wavelength, and is equal to or smaller than three wavelengths. In addition, amplitude and phase changing devices 83 for changing the amplitudes and phases of signals inputted from the antenna elements 81 via frequency converters 82 are provided in respective antenna input units. Further, an amplitude and phase calculator 84 calculates the amplitudes and phases of the respective antenna input signals so that an error between a signal previously known on the reception, and a combined signal of the signals received at the antenna elements 81 is minimized. Then, the amplitude and phase calculator 84 adjusts the respective amplitude and phase changing devices 83 so that the amplitudes and the phases of the respective antenna elements 81 calculated by the amplitude and phase calculator 84 can be outputted from the amplitude and phase changing devices 83.
In the antenna apparatuses according to the prior arts, omni-directional antenna elements are mainly used. Therefore, the degree of freedom of the antenna elements corresponding to the number of the formed nulls in a radiation pattern is only N−1 when the number of the provided antenna elements is N larger than one. Therefore, a problem has been caused that a larger number of antenna elements are required for the antenna apparatuses in order to direct the nulls toward the human body and the interference waves.